The present invention relates to an object detection sensor which can be used as an automatic door sensor and the like. In particular, the present invention is concerned with measures to increase the degree of freedom in the setting of a detection area.
As an example of the conventional automatic door sensor, Japanese Patent Laid-open Publication No. H7-229972 discloses an active infrared sensor, as shown in FIG. 10, which is equipped with a transmitter and a receiver. In this infrared sensor 101, while the transmitter emits infrared light toward a predetermined detection area 102 (defined by a chain-dotted line in FIG. 10), the light is reflected and received by the receiver. If a person or like object enters the detection area 102, the receiver receives the infrared light in a different state. The sensor 101 detects this change as approach of an object to an automatic door 103. On detection of the object, the sensor 101 sends an object detection signal to an automatic door controller (not shown), so that the automatic door controller starts a door driving source (a driving motor) to open the automatic door 103.
In some applications of the active infrared sensor, detection of objects may be partially unnecessary in the detection area 102. Such a no-detection area is provided by masking. By way of example, the detection area 102 in FIG. 10 has a near-square contour as viewed in plan view. In this detection area 102, a shaded area 104 on the floor can be masked by emitting no infrared light toward the mask area 104. Alternatively, while infrared light is emitted to the entire detection area 102, the light reflected in the mask area 104 may be cancelled in a signal processing.
Another type of automatic door sensor is an image sensor which is equipped with a camera having a built-in image pickup element (e.g. CCD). This image sensor utilizes the camera to take an image of a detection area, and, based on the image information, judges the presence or absence of an object in the detection area. Also in the image sensor, the detection area may include a part where detection of objects is not required (a mask area). The mask area can be obtained by taking no image of the mask area or by cancelling the image of the mask area in a signal processing.
Nevertheless, these conventional sensors have following problems.
Referring to FIG. 10, when the mask area 104 is set in the infrared sensor, a mask space 105 is created over the area 104 (as defined by dashed lines). In other words, setting of the mask area 104 is inevitably accompanied with a mask space 105 which assumes the contour of a substantially quadrangular pyramid with the base of the mask area 104. The contour of the mask space 105 depends on the position of the infrared sensor 101 (the sensor in FIG. 10 is mounted on the transom) as well as the position and contour of the mask area 104. Therefore, it is impossible to set the mask area 104 on the floor (the two-dimensional mask area on the floor) separately from the mask space 105 (the three-dimensional mask area in the infrared light emission space). This restriction has been an obstacle to increase the degree of freedom in the setting of a detection area. A similar problem arises when the image sensor sets a mask area.
Turning to FIG. 11, the infrared sensor sets the detection area 102 on the floor to have a depth E (the sidewise dimension in the drawing), in an attempt to detect a person or the like that enters the range of the depth E. In operation, however, the detection sensitivity is low along the end of the detection area 102 (e.g. the area indicated as the depth E1 in the drawing). Hence, in order to ensure a high detection sensitivity at the end area, the depth of the detection area 102 on the floor is generally set greater than the required depth E, as far as the depth E2 in the drawing.
In this case, however, a sensor 106 may detect an object which is present at the outside of the required detection area (the range of the depth E), which causes misoperation of the automatic door. For example, referring to FIG. 11, suppose that the detection object is a person passing on a pavement, and that the depth E corresponds to the pavement. It is further supposed that a driveway is adjacent to the outside of the depth E. In this situation, if the detection area 102 is set greater than the depth E, the sensor 106 detects a vehicle 107 travelling on the driveway, and unnecessarily opens the door whenever a vehicle 107 passes through the detection area 102.
The present invention is made in view of these problems. An object of the present invention is to provide an object detection sensor which is capable of setting an optional detection area and preventing improper detection.
In order to accomplish this object, the present invention takes an image of a detection area by image pickup means such as a CCD camera. In this image, the distance to an object is calculated. Based on the calculated distance, the sensor detects the three-dimensional position of the object in the image space, and compares the detected position with an object detection space which is registered in advance. Through this process, the sensor identifies the presence or absence of an object within the object detection space. In addition, the object detection space can be set in an optional three-dimensional contour.
An object detection sensor corresponding to claim 1 (hereinafter mentioned as Invention 1) is equipped with image taking means, distance calculation means, position detection means, detection space registration means, judgement means and output means. The image taking means is capable of taking an image of a predetermined image space. The distance calculation means calculates a distance between the image pickup means and an object observed in the image of the image space, on receiving an output from the image pickup means. The position detection means detects a three-dimensional position of an object in the image space, on receiving an output from the distance calculation means. In this position detection means, the position of an object is detected with respect to the object for which the distance from the image taking means is calculated, based on the calculated distance. The detection space registration means is capable of setting an optional mask space in the image space which is covered by the image taking means. This detection space registration means registers a space in the image space, excluding the mask space, as an object detection space. The judgement means judges whether the detected three-dimensional position of the object locates within or outside the registered object detection space, on receiving outputs from the position detection means and the detection space registration means. The output means outputs an object detection signal, on receiving an output from the judgement means. This object detection signal is produced, with a proviso that the detected three-dimensional position of the object locates within the registered object detection space.
An object detection sensor corresponding to claim 2 (hereinafter mentioned as Invention 2) adopts a different type of detection space registration means. This detection space registration means registers, as an object detection space, an optional space in the image space which is covered by the image taking means.
According to these features, when the image pickup means takes an image, the distance calculation means calculates the distance between the image pickup means and an object observed within the image. Based on the information, the position detection means detects the three-dimensional position of the object. On the other hand, the detection space registration means registers an object detection space which is set in an optional three-dimensional contour by a user. The judgement means judges whether the detected three-dimensional position of the object locates within or outside the registered object detection space. If the object is present within the object detection space, the output means produces an object detection signal. For example, where this object detection sensor is applied to an automatic door, the door is made open in response to the detection of an object.
An object detection sensor corresponding to claim 3 (hereinafter mentioned as Invention 3) is featured by a specific manner of setting the object detection space which is registered in the detection space registration means. Namely, the image space covered by the image pickup means is divided into a plurality of space elements in a cubic lattice pattern. As the object detection space, the detection space registration means registers a space which is composed of a part of these space elements.
With this feature, a user can optionally set the three-dimensional coordinates of space elements which correspond to an object detection space, considering which of the space elements in the image space should constitute to the object detection space. Thus, it is possible to set the object detection space in an optional contour, simply by setting the coordinates of some space elements.
With respect to any of Invention 1, Invention 2 or Invention 3, an object detection sensor corresponding to claim 4 (hereinafter mentioned as Invention 4) is featured by a specific operation of the output means for producing the object detection signal. In detail, this object detection sensor is installed as a sensor for an automatic door and associated with means for controlling an open/close drive of the door along the track. The output means is arranged to be capable of outputting the object detection signal to the door drive control means, such that the object detection signal outputted to the door drive control means causes the door to open fully.
Owing to this feature, the detection area around the door can be set in an optional contour. As a result, the object detection sensor can avoid improper detection and thereby improve the reliability in the opening/closing action of the automatic door.
With respect to any one of Invention 1 to Invention 4, object detection sensors corresponding to claim 5 and claim 6 (hereinafter mentioned as Invention 5 and Invention 6, respectively) are featured by specific operations of the distance calculation means for calculating the distance between the image pickup means and the object. Namely, the sensor of Invention 5 employs image pickup means which has a plurality of image pickup elements. In this sensor, the distance calculation means calculates the distance between the image pickup means and the object by stereo image processing which utilizes parallax of images taken by these image pickup elements.
On the other hand, the sensor of Invention 6 employs image pickup means which has a variable focus lens. In this sensor, the distance calculation means calculates the distance between the image pickup means and the object, based on the degree of focus on the object which is observed in the image taken by the image pickup means.
These features enable accurate calculation of the distance between the image pickup means and the object. In particular, the sensor of Invention 6 can simplify the structure of the image pickup means, because it requires no more than one image pickup element.